The present invention relates to surface conditioning articles formed from an organic matrix coated and engulfed by organic binders. The present invention also relates to a method for making a layered composite from which a surface conditioning article may be machined.
Surface conditioning articles are surface treatment articles formed from an organic polymeric matrix formed of a solid or foamed organic polymer or a nonwoven fiber web find utility in treating a surface to prepare it for further coatings. Burrs and flashing from cast, drilled or punched parts must be removed to produce a desired shape or surface finish. Surface conditioning articles in the form of wheels, discs, or belts operating at high speeds and high pressures must have sufficient strength and durability when subjected to high use pressure against the workpiece. It is desirous for the article to be flexible to intrude into crevices in the workpiece. In addition, the propensity of the article to smear onto the workpiece must be taken into consideration. Smearing is generally considered deleterious.
As used herein the term xe2x80x9csmear-resistantxe2x80x9d is meant to denote embodiments of the invention exhibiting substantially no visible signs of the surface treatment article remaining on the workpiece after the workpiece article has been treated. The articles of the invention call be urged against a workpiece at high operating speeds and/or pressures without smearing of the article onto the workpiece. The term xe2x80x9csurface conditioningxe2x80x9d is used here to include all steps between preliminary removal of material and final polishing or finishing step. Those steps comprise, grinding, lapping, deburring and the like.
Polymeric resinous binders used to bond the matrix or to secure abrasive particles within the matrix of such products have generally been either of the hard thermosetting type or the strong, tough elastomeric type. Hard thermosetting resins, such as base catalyzed phenol formaldehyde, are widely used to secure abrasive particles to sheet-like backing or to the fibers of a nonwoven web. Such hard resin binders, while usually having high tensile strength, low elongation at break or failure, and resistance to significant change when subjected to elevated temperatures, are undesirably susceptible to brittle fracture. Strong, tough elastomeric resin binders are more desirable in certain applications which require tougher, more durable surface treatment products. Such elastomeric binders have excellent tensile strength, a very high elongation at break, and resistance to brittle fracture but may exhibit significant softening at elevated temperatures as might be encountered when the surface treatment article is urged against a workpiece at high speeds and pressures. Such softening may result in smearing or transfer of portions of the article to the surface of the workpiece, which as described previously is not desired by the user.
The surface conditioning industry is continually striving for articles which more closely meet user demands. In addition, methods of producing surface conditioning articles that are kind to the environment, particularly the air and water, are especially strived for.
In light of the above user-driven demands it would be advantageous if surface conditioning articles could be developed which, by virtue of simple adjustment of binder ingredients, can be tailored to be flexible, substantially non-smearing at use pressure and temperature, all while using water-base formulations in the manufacturing processes which do not require use and subsequent removal of volatile organic hydrocarbons.
Specific properties needed for the coatings are linked to the final product applications. The product has to be flexible to be used in narrow and short belts form for example; it has to be conformable to allow uses on complicated surfaces; it has to be resistant to abrasion, and has to show resistant to brittle fracture to avoid an excessive wear of the product when used. It has to be resistant to high temperature occurring when used at high pressure/speed, and has not to let any smearing coating on the treated surfaces.
The standard reference product currently existing is made with urethane resins used in a solvent based system and catalyzed with an MDA (methylene dianiline). Several trials have been run to find a water base alternative to this resins use.
These articles have been made by the following generally known scheme. A first or xe2x80x9cprebondxe2x80x9d coating of a binder precursor solution without containing abrasive particles, which includes one or more of the above-named resins, is coated on the web and cured by, exposure to heat in order to impart sufficient strength to the nonwoven web for further processing. Then a xe2x80x9cmakexe2x80x9d or xe2x80x9cslurryxe2x80x9d coating based on a resinous organic binder is applied to the web to secure fine abrasive grains throughout the lofty fibrous mat and cured. Thereafter, a xe2x80x9csizexe2x80x9d coating of resinous binder material and abrasive particles is applied, usually by spray-coating, over the prebonded web to increase the abrasive characteristics of the article, such as preventing the abrasive mineral from shelling. Then, the size coating is cured. The resins of the various xe2x80x9cprebondxe2x80x9d, xe2x80x9cslurryxe2x80x9d, and xe2x80x9csizexe2x80x9d coatings may be different.
The use of solvent-coated crosslinked urethanes in the xe2x80x9cprebondxe2x80x9d provides the requisite elasticity and protect nylon fibers of the web from attack by subsequently applied phenolic make coates used for bonding of mineral abrasive into the web.
The prebond coat is the most important one as far as smear resistance is concerned, because it protects the fibers from softening when using the article in heavy, high pressure.
Phenolic resin binders, in particular, are used extensively to manufacture nonwoven abrasive articles as a binder for the abrasive particles because of their thermal properties, availability, low cost, and case of handling. The monomers used in greatest volume to produce phenolic resins are phenol and formaldehyde.
In order to reduce emissions of xe2x80x9cVOCsxe2x80x9d (volatile organic compounds), it has been suggested to increase the water compatibility of phenolic resins. J. D. Fisher, in an article entitled xe2x80x9cWater Compatible Phenolic Resinsxe2x80x9d in Proceedings of the American Chemical Society, Division of Polymeric Materials: Science and Engineering; no. 65, pp. 275-276 (1991), describes methods of making xe2x80x9cwater compatiblexe2x80x9d phenolic resins, their benefits, and their shortcomings.
Also, a compatibility problem arises from the use of the phenolic binder in particular together with a nonwoven web based on polyamide fibers. A particularly useful known nonwoven abrasive article is one comprising a web of polyamide fibers and resole-type phenolic resins as the curable binder. Such a composition provides for strong, tough, temperature resistant abrasive articles that may be made economically.
Rubber-modified phenolic resins have also been used in the manufacture of nonwoven abrasive articles, such as in the disclosure of commonly assigned U.S. Pat. No. 2,958,593 (Hoover et al.), as an optional rubber treatment disposed on one side of the structure to increase the resistance of the overall abrasive article structure to tearing and shredding. For example, Hoover et al. exemplifies a nylon fiber web being first coated with a phenol-formaldehyde and amine terminated polyamide resin-containing coating, followed by transmitting the phenol exposed web to a curing oven where the coated web is so heat-treated such that the emitted treated web is cured to a nontacky state while still warm, and, only thereafter, a rubbery composition based on a butadiene acrylonitrile copolymer latex (viz. trade designation xe2x80x9cHYCAR LATEX 1561xe2x80x9d, from B.F. Goodrich Co.) is applied to the opposite side of the web and heat-cured in an oven.
The modification of a phenolic resin precursor system used for binding, lower tenacity polyamide web fibers by the presence of a low rate of butadiene acrylonitrile latex, less than 40%, as a modifier agent therewith which alleviates the degradation of polyamide fibers in the presence of phenol, has been disclosed in U.S. Pat. No. 5,591,239. In this patent, the function of the latex is to improve the mechanical characteristics of a phenolic impregnated web and especially reduce the tearing of the open low-density nonwoven abrasive article.
The goal of the present invention is to provide surface conditioning articles which can be urged against a workpiece at high pressure and/or high speed with no undesirable smearing or other transfer of the article to the workpiece surface. The goal of the present invention is further to provide a surface conditioning article prepared with water-based formulations, said article having properties, especially, flexibility and smear resistance, equivalent to polyurethane standard reference article currently existing.
Water-based formulations for surface treating products having a wider range of possible use than the specific surface conditioning article of the present invention, have been disclosed in U.S. Pat. No. 5,306,319. The water-based formulations of U.S. Pat. No. 5,306,319 comprise binders consisting in a reaction product of polyurethane prepolymers or plurality of adducts. These adducts render the preparation method difficult and costly. Moreover, the properties do not totally respect all of the customers needs defined as xe2x80x9ccutxe2x80x9d, xe2x80x9cwear resistancexe2x80x9d, xe2x80x9csmear resistancexe2x80x9d and xe2x80x9cflexibilityxe2x80x9d for the specific field of the surface conditioning article.
Another goal of the present invention is therefore to provide new water-based formulation is particularly useful as surface conditioning article, having a decrease in the products costs in respect of those disclosed in U.S. Pat. No. 5,306,319.
For doing this, a first aspect of the invention is a surface conditioning article comprising an organic matrix substantially engulfed by water-based organic binders including a first or xe2x80x9cprebondxe2x80x9d binder and a second or xe2x80x9cslurryxe2x80x9d binder with abrasive particles dispersed and adhered within said second binder, wherein the first binder comprises a mixture of a phenolic resin and a carboxylated butadiene-acrylonitrile copolymer latex, in the range of weight ratio of dry materials of said latex versus said phenolic resin of 90/10 to 60/40.
Phenolic resin provides hardness, cohesion, adhesion of the fiber web and between different layers, high thermal resistance to the coating, it is a perfect support for the layers which include minerals in abrasive applications. Phenolic may be too brittle and too hard to be used alone in an alternative coating to urethanes. Specificity of the phenolic resin used is preferably to present very high water tolerance to allow to support to be mixed with very high ratio of NBR latex dispersion and this without getting mixing compatibility problems (gellification). That is why it is necessary to have a phenolic resin no too much advanced in the condensation reaction (i.e. with a low molecular weight). Specific experiments have been needed to determine phenolic resin compatibility to NBR latex.
In a preferred embodiment, the said phenolic resin of the first binder is a resole-type phenolic resin with a water tolerance of at least 500% by weight. More particularly, the water tolerance comprises from 500 to 2500%. A water tolerance of 500% by weight means that the resin can be mixed with 5 times its own weight with water without precipitations.
In a preferred embodiment, said phenolic resin of the first binder has a molecular weight in the range of 100 to 1000.
An important function of the carboxylated butadiene-acrylonitrile latex (herein after referred to as xe2x80x9cNBRxe2x80x9d latex) in the present invention is to provide outstanding thermal resistance for a so flexible coating. This protects the fibers from softening at high temperatures. This gives to the final product flexibility and smearing resistance in the same time. This function is linked to the way carboxylated NBR latex degrades with temperature-cyclize before being destroyed by heat by, melting-in contrast to systems where such a cyclisation is not possible. They show no residual thermoplasticity whatever; that makes for example NBR latexes highly suitable items for brake lining and clutch plate facings.
NBR latex provides high flexibility (Tg close to xe2x88x9230xc2x0 C.), conformability, softness, and very high resistance to flex fatigue and very good mechanical properties for such flexible coatings. It shows high resistance to abrasion and wear. It keeps high flexibility at low temperatures. In view of all these properties, it is preferred to use a carboxylated NBR latex with high acrylonitrile ratio especially wherein the said butadiene-acrylonitrile latex has a molar percentage of acrylonitrile of at least 25%. More particularly the molar percentage of acrylonitrile is from 25 to 35%.
In a preferred embodiment, the latex particles have a size in the range of 10 to 500 nm.
The articles of the invention have a wide available range of flexibility and smear-resistance, thus making them useful in articles designed to abrade a workpiece, deburr a workpiece, wipe the surface of a workpiece, or buff a workpiece. In addition, the inventive binder is applied to the organic matrix in the form of an aqueous composition, thus eliminating or substantially reducing the release of volatile organic compounds in the process of making the inventive articles. The carboxyl groups allow self crosslinking of the copolymer without use of catalyzing agent.
In one embodiment, the organic matrix comprises an open, lofty, three-dimensional nonwoven web of the article which comprises a plurality of organic polymeric fibers bound together at points where they contact by the first binder.
In a preferred embodiment of the present invention, the article comprises a third or xe2x80x9csizexe2x80x9d binder coated over the second binder, said third binder comprising a mixture of phenolic resin and carboxylated butadiene acrylonitrile copolymer latex.
More preferably, the weight ratio of dry materials of said latex versus said phenolic resin in the third binder is in the range of 60/40 to 40/60.
In one embodiment, the phenolic resin and carboxylated butadiene-acrylonitrile latex are the same in the first and third binders.
The phenolic resin of the first and third binders may be selected from commercial materials.
In particular appropriate embodiments of the present invention, the phenolic resin of first and third binders may be selected from the group consisting of phenolic resins commercially available under the trade designations xe2x80x9cLACFEN420xe2x80x9d (from Satef Huttens Albertus Spa) and xe2x80x9cSW 378xe2x80x9d (from Bakelite) and the butadiene-acrylonitrile latex is selected from the group of butadiene-acrylonitrile latexes commercially available under the trade designations xe2x80x9cPERBUNAN N2890xe2x80x9d (from Bayer) and xe2x80x9cLN 240Sxe2x80x9d from BASF.
The second binder of the article according to the present invention may comprise conventional water-base resole-type phenolic resin.
Another aspect of the invention is a method of making a layered composite from which a surface conditioning article according to the present invention may be machined, the method comprising:
a) coating a major portion of the organic fibers of an open, lofty, three-dimensional nonwoven web with the first binder composition to form a first coated web;
b) exposing the first coated web to energy sufficient to at least partially cure the first binder composition to form an open, lofty, three-dimensional nonwoven prebonded web of fibers;
c) coating at least a portion of the fibers of the prebonded web with an aqueous slurry, comprising water, abrasive particles and a said second binder to form a second coated web;
d) exposing the second coated web to energy sufficient to cure the second binder;
e) coating at least a portion of the fibers of the second coated web with a third binder;
f) exposing the third coated web to energy sufficient to cure the third binder, remove substantially all the water, thereby forming a substantially dried web;
g) juxtaposing a plurality of substantially dried webs of step g) to form a precursor layered composite; and
h) compressing the precursor layered composite with pressure and at a temperature sufficient to form the layered composite.
In one embodiment before step a), the method comprises:
1) forming an open, lofty, three-dimensional nonwoven web of organic fibers; and optionally
2) entangling the organic fibers of the nonwoven web to form all entangled web having an effective density.
Preferred are those methods wherein the layered composite is machined into the form of a surface conditioning article, in the form of a disc, wheel, endless belt, rectangular block, and the like.
The nonwoven web may be selected from commercial materials.
However, another aspect of the invention is a method of making an open, lofty nonwoven surface conditioning article, wherein the step a) comprises two sub-steps:
a) forming an open, lofty, three-dimensional nonwoven web of organic fibers; and
b) entangling the organic fibers of the nonwoven web to form an entangled web having an effective density.
Surface conditioning articles of this inventions are suitable for use in a variety of applications. They may be adapted for use on any workpiece composition including metal, wood, plastics, composites, glass, ceramics, concrete, and others. They are designed for a use intermediate between the aggressive removal of material from a workpiece and clean a workpiece in preparation for painting, plating, etc.
Surface conditioning articles of the invention are especially effective in conditioning metals without substantial smearing onto the metal workpiece.
When the surface conditioning article of the invention is rotated against a workpiece under heat-generating conditions such as high wheel to workpiece pressure and surface speed, these conditions do not cause surface portions of the wheel to smear, or transfer onto the surface of the workpiece.
An important aspect of the invention is that articles of the invention employ inventive binders which allow the articles to exhibit a high flex fatigue resistance (in other words, able to deform and penetrate into grooves and indentations in a metal workpiece, and then return to its original shape, in a cyclic process).
The binders may contain optional functional additives or fillers such as colorants, thickening agent, pH buffering agent and scavengers. As previously stated, binders are applied to the organic matrix in the form of aqueous compositions (emulsions, dispersions, or slurries). The aqueous compositions may comprise plasticizers, viscosity modifiers, grinding aids and abrasive particles, the latter in the case of aqueous slurries.
Thickeners may be used to adjust the viscosity of the aqueous or solvent dispersed binder system, i.e., when in the liquid state, in order to provide for an easily-coatable composition. Examples of suitable thickeners include salt of polyacrylic acid carboxymethyl cellulose, guar gum, gum tragacanth, homo- and copolymers of poly(vinyl alcohol), methyl cellulose, modified starch, and the like. The thickening agent increases viscosity of the wet mix so that sufficient weight can be applied with a roll coat process on the fiber web.
Suitable pH buffering agents may include materials like triethanolamine and ammonia. pH buffering agent helps thickening efficiency without leaving residual basic component in the wet coating during drying.
Suitable scavengers may include materials like urea, or melamine. Scavengers minimize formaldehyde emissions of phenolic resins during drying.
Examples of colorants are inorganic pigments, organic dyes, and the like. Reinforcements may include, for example, short organic or inorganic fibers, spheres, or particles. Grinding aids may be materials such as poly(vinyl chloride), potassium fluoroborate, and the like. Fillers may include calcium carbonate, fumed silica, and other materials which are primarily inert with respect to the utility of the articles. Plasticizers may include, for example, phthalic acid esters, oils, and other relatively low molecular weight materials.
Abrasive particles are added to the binder system to render the inventive surface conditioning article more aggressive in its action on a workpiece. Such abrasive particles, employed to produce the surface conditioning articles of the present invention, may be any known abrasive material commonly used in the abrasive art. The abrasive granule size and type may be any of those commonly used to make surface conditioning articles. Examples of suitable abrasive particles include silicon carbide, aluminum oxide, cerium oxide, alumina zirconia, cubic boron nitride, garnet, pumice, sand, emery, mica, flint, talc, corundum, quartz, diamond, boron carbide, fused alumina, sintered alumina, alpha-alumina-based ceramic material (available from Minnesota Mining and Manufacturing Company, Saint-Paul, Minn. under the trade designation xe2x80x9cCUBITRONxe2x80x9d), and mixtures thereof. Agglomerate abrasive particles, such as those described in U.S. Pat. Nos. 4,652,275 and 4,799,939 may also find utility. Softer abrasive particles such as those made of thermoplastics or thermosetting material glass as well as other softer abrasive particles may be used for polishing applications. It is considered within the skill of the artisan to select the appropriate abrasive material for the particular use without undue experimentation.
The organic matrix serves the function of providing strength and structural integrity to the surface conditioning articles of the present invention. On a more fundamental basis, the organic matrix serves the function of providing a substrate for the binders and abrasive particles.
The organic matrix may be either a solid of foamed organic polymer or a nonwoven web comprised of organic fibers, preferably hydrophilic organic fibers. If hydrophilic organic fibers are employed, a heating step may be eliminated or reduced as the fibers will absorb water from the emulsified binder. An example of a lofty, nonwoven web formed of crimped staple fibers adhered at points of contact with binder which contains abrasive particles is taught in U.S. Pat. No. 2,958,593 (Hoover et al.). U.S. Pat. No. 4,227,350 (Fitzer) discloses a matrix formed of three-dimensionally undulated inter-engaged autogenously bonded continuous filaments.
The organic matrix may be comprised of thermoplastic organic staple fibers, such is nylon (polyamide), polyester, and the like staple fibers or a combination of thermoplastic and cellulosic staple fibers, such as viscose rayon, and the like. Preferred thermoplastic fibers are nylon staple fibers, especially nylon 6,6. If a combination of thermoplastic organic fibers and cellulosic fibers are employed the weight of cellulosic fibers as a percentage of the total fibers weight may range from about 5 weight percent to about 50 weight percent.
In a preferred embodiment, said open, lofty, three-dimensional nonwoven web comprises organic polyester or polyamid fibers.
The fibers preferably have denier ranging from about 10 to 100 and length ranging from about 10 to 100 mm.
Surface conditioning articles within the present invention may take any of a variety of conventional forms such as sheets, blocks, strips, belts, brushes, rotary flaps, discs, or solid or foamed wheels. Especially useful forms are wheels in the form of a disc or right circular cylinder having dimensions which may be very small, e.g., a cylinder height on the order of a few millimeters, or very large, e.g., two meters or more, and a diameter which may be very small, e.g., on the order of a few centimeters, or very large, e.g., one meter or more. The wheels typically have a central opening for support by an appropriate arbor or other mechanical holding means to enable the wheel to be rotated in use. Wheel dimensions, configurations, means of support, and means of rotation are well known in the art. A useful summary of various wheel forms of surface treatment articles which may be made using the inventive binders are described in the publication xe2x80x9c3M Wheelsxe2x80x9d, published in 1990 by Minnesota Mining and Manufacturing Company, Saint Paul, Minn. (xe2x80x9c3Mxe2x80x9d), which is incorporated herein by reference.
Surface treatment articles of the present invention in which the organic matrix is engulfed by a binder may be prepared by forming a layered composite. Layered composites (known in the art as xe2x80x9cslabsxe2x80x9d) may be produced by cutting, punching, or otherwise machining uncured or partially cured webs into sheets or discs which are then overlapped on one another and then compressed and cured to make a higher density, slab. Such cutting, punching and other machining techniques are well known to those skilled in the art.
A layered composite may be used as the source of a multitude of articles of the invention each having various diameters, or all the same diameter, as required by the user. Article of the invention may be produced form the layered composites by machining using appropriate techniques which are also well known in the art. For example, a wheel shape may be die cut from a slab of the layered composite. Additionally, ribbons, strips, or elongate segments of the layered composite may be spirally wound into a wheel shape while the binder is uncured or partially cured and then fully cured to yield a wheel.